High Performance Cylinder Heads??

[Highside]

I have been toying with the idea of casting a head for the XS. Instead of going radical, it'll just be a refinement of the stock design; less valve angle and smaller ports and chambers.

I want to use a stock style camshaft so it would need shorter rockers to accommodate the narrower valve angle. That has been my latest hangup. Can anyone suggest a bike (or car) with suitable rocker arms?

I can't help you with stock parts, but I have a friend and former co-worker, who can make you top notch rocker arms. Darrel Reid makes what is arguably the best rocker arm for NHRA Top Fuel Dragsters. His prices are very reasonable for top quality stuff. AFAIK, he's kinda busy right now, but he might be able to take on your project before the racing season ends. If you call him, tell him Eric sent you.

 

[dwyatt]

Yup, the head design has always been know to be crap, but it is what it is. The 650 Central head is a cnc copy of the last factory Yamaha racing heads, ported by Lilly. Got it, love it due to the heritage, not the technology. If you ride an XS650 for it's speed potential, you'll alwys be frustrated. Still a way cool scooter.

 

[xstra]

The 650 Central heads aren't a copy of the factory racing heads as the castings are completely different. They attempt to replicate some of the modification specs used on production heads.

 

[dwyatt]

Not the OW heads,no, Before starting the OW project to design a proper flowing head, Yamaha used ported OEM heads for years.

 

[Jack]

Well, after getting my hands on an XS650 cylinder head and taking a close look at it, I can see right away some of the performance restrictions built into it.

The valve angles are too steep, resulting in a chamber that is too large. You can't get good CR's without risking detonation or combustion dead spots (maybe that's why they went with the cast iron chamber inserts?).

The exhaust port is poorly designed. It starts its horizontal bend right before the valve guide, causing bad flow bias around the valve stem. To compensate for this, they made the exhaust valve too big and gave the port too much cross sectional area for the airflow requirements. With some heavy meatball surgery, I bet I can get this port to flow the same, or better, while reducing its volume.

650 Central.com sells a head for $1400 which it claims is the best thing on the market. For that price, you could almost make a custom billet head that would solve the design flaws of the stock head and make 70+ HP with little effort.

Are there any other high performance heads on the market for the XS650??

For an old dinosaur engine that has had it's nuts and bolts turned by some most talented racers for decades by the likens of Shell Thuet,Bob Bertaut,Three M,Craig Hanson Racing,Tilley and who ever else I've accidentally left out where all able to coach respectable flow gains from the XS head even with the inherited casting flaws to yield 70 plus HP which isn't to shabby if you ask me. You simply don't need A BILLET head on the Xs650 to have fun,you just need to educate yourself on what makes the XS head tic. It doesn't take much effort to achieve a 15% intake flow a and 25 % exhaust flow gain but let me give give a little tip,where ever you obtain a gain ,you will encounter a lose somewhere else in the flow curve,just the nature of overall head design limiting the efficiency of the port,you just need to make the best of it and port the head to cam lift.
And one more thing,if the ports are so over sized as you state,isn't it odd that these old dinosaurs are knocking down 44,50 plus and even 65 plus miles per gallon in stock form or modified. In a racing situation,then yes it might be beneficial to modify the ports to yield higher outputs or tailor the engine to track conditions.

 

[Patches]

I've researched this topic extensively. There are many in depth threads about this in the 650 garage.

If the gentlemen posting above me is the Jack that I think it is, he knows his shit. Probably as much or more than anybody around in terms of the XS650 head and performance porting for this head.

Jack- if you are reading this do you have any idea what happened to the pictures and info in the porting thread you had in the 650 Garage forum?

 

[L_Brown]

I found this

http://thexscafedotcom.wordpress.com/2011/09/13/xs650-ouow72-heads/